Different weight bullets vs. coal

[Silentstalker]

So over the winter I want to test the 130 gr. series of nosler bullets in my .270 win. My questions hopefully are easy ones.

Will the 130 BT typically like the same coal as my current 150 BT, same question for the Partition?

Is so I could in theory load the 130's to the same coal as the 150 and only mess with powder charge at least to start with. My BT load is under 3/4" and my PT load is right at an inch.

If I try the E-tip also, should I start with the BT coal and go from there? Should I go straight to the E-tip and use it with the higher BC and same Sect. Density?

If for some reason I strike gold with the 130's they would be used for all around ammo. Antelope, mule deer, cow elk, and occassional bull elk and whitetail.

Thanks again for your insight and help!

 

[steve4102]

It depends, If you are measuring OAL off the Ogive with a comparator, Maybe. If you are measuring your OAL off the bullet tip, not so much.

 

[DrMike]

Will the 130 BT typically like the same coal as my current 150 BT, same question for the Partition?

Not necessarily. You will need to test each load whenever you alter a component. Altering a parameter on a bullet introduces new variables such as bearing surface, bullet jacket thickness, etc. It is possible that the harmonics will be similar, and you won't find it necessary to alter COAL, but you can't predict this to be the case w/o some extensive mathematical calculations. Construction of the PT differs quite a bit from the BT, and that can introduce a variable. Long story short, if I were starting the loads you suggest, I would begin at the OAL you now have and adjust as necessary. However, I would know that changing the COAL is a possibility.

If I try the E-tip also, should I start with the BT coal and go from there? Should I go straight to the E-tip and use it with the higher BC and same Sect. Density?

E-Tips, having a totally different construction, will likely require a significantly different COAL. In my experience, monolithic bullets such as the E-Tip, give the best accuracy when they have quite a bit of jump to the lands. Ballistic Tips and even Partitions, with their cup-and-core construction, tend to perform best with a relatively short jump to the lands. I generally begin testing for E-Tips at 0.050 inches off the lands. It is common that the first node found with many of my E-Tip loads (and TSX loads) will be in the vicinity of 0.100 inches off the lands.

 

[Partisan]

Here are some OAL measurements to touching the lands for my 7mm Rem. These were using Hornady's OAL tool.
The measurement for the 160 & 175 partitions are an average of 3 bullets to allow for variance in the soft lead tips.

154gr SST 3.380
150gr E-Tip 3.335
150gr. B-tip 3.400
160gr Part. 3.295
175gr Part 3.300

These are for a single rifle with it's history of barrel usage and erosion. But it illustrates that each bullet will vary in jump when load to the same COAL. Only measuring will tell you what the relation to the lands will be.

Hornady suggests that a good jump for one bullet is a good place to begin for a different bullet. But that is just a start.
The E-Tips and the Monolithic bullets are a whole different ballgame though.

 

[Silentstalker]

Great info! Once again, thank you!

 

[hubcap]

Acually Silent stalker, I have been quite successfull using the same coal with nosler bullets. In my ,270 I do use the same length for the 130 BT,140BT and 150 BT. I simply add or subtract the powder charge in small increments of.2 grains looking for the best groups. Keep in mind the bullet jump is not the same using that method. No matter it has worked out fine for me. Essentially I do the same thing with AB,s and PT,s. My rifle is rather long throated and has a small amount of throat erosion. Therefore it is out of the question loading close to lands. I use alot of bullet jump in this rifle. In my other .270 which is shorter throated I acually load everything alot closer to lands because I can. In this rifle everything Dr. Mike already stated is the case. PT and BT, about .030 off the lands and dial the load in with the powder adjustments. Both rifles seem to shoot there best with AB,s using more bullet jump than the PT and BT. In general with the .270 there is not alot of weight difference between the 130,140 and 150 bullets. Once I discover a seating depth that fits the magazine and gets me moa or better I simply play with charge from that point on with all three bullet weights.

 

[Silentstalker]

Good to know hubcap. I am going to start at my current coal for each respectively and modify .2 grs. As necessary to dial them in. Thanks for your intel!

 

[magothy1]

Along the same lines, I have a load for my 7 mm mag with 140 gr Etips that's working pretty well. If I go to 150 gr Etips would I use the same length OAL to give me the same comparator length ?